This case describes a method for utilizing a reference detector such that a proper light power level and light viewing area of a photo detector array is maintained on a surface when triangulation data is obtained. Central to this invention is the use of a reference detector such as a photodiode (eg. a UDT PIN6-D) whose length (area) is the same or less than the length (or area) of a linear (or matrix) photo detector array (or other image position sensing photodetectors such as a UDT SC-10 analog type) used to determine spot, line or other zone position projected onto a part surface and imaged onto the array. Typical arrays are the Reticon 256G (linear) and GE TN2500 (matrix).
Use of such a reference detector allows the presense of the surface to be found from the output of the detector and the linear sensor movement axis (or axes) slowed down so that the measurement can occur. This is for rapid advance toward a part surface where the diode array scan rate would not be fast enough to precisely catch the point in question. This also provides the best possible compensating signals for the array since the array is looking at the same zone on the part that the reference detector sees. These compensating signals are used to maintain a substantially constant amount of energy on the array and thereby allow consistent readout of spot or other zone image position independent of surface reflectivity, scattering properties, etc.
Finally, when the reference detector is smaller than the array, one can assure that the spot or line image has to be on the detector array completely before the reference detector picks it up.